This disclosure relates in general to copier/printers, and more particularly, to cleaning residual toner from an imaging device surface and reducing cleaning blade failure by controlling blade stress incurred due to increasing coefficient of friction.
In a typical electrophotographic printing process, a photoreceptor or photoconductive member is charged to a uniform potential to sensitize the surface thereof. The charged portion of the photoconductive member is exposed to a light image of an original document being reproduced. Exposure of the charged photoconductive member selectively dissipates the charges thereon in the irradiated areas. This process records an electrostatic latent image on the photoconductive member corresponding to the informational areas contained within the original document. After the electrostatic latent image is recorded on the photoconductive member, the latent image is developed by bringing a developer material into contact therewith. Generally, the developer material comprises toner particles adhering triboelectrically to carrier granules. Toner particles attracted from the carrier granules to the latent image form a toner powder image on the photoconductive member. The toner powder image is then transferred from the photoconductive member to a copy sheet. Heating of the toner particles permanently affixes the powder image to the copy sheet. After each transfer process, the toner remaining on the photoconductor is cleaned by a cleaning device.
Blade cleaning is a technique for removing toner and debris from a photoreceptor, photoconductive member, or other substrate surface within a printing system. In a typical application, a relatively thin elastomeric blade member is supported adjacent to and transversely across the photoreceptor with a blade edge that chisels or wipes toner from the surface. Toner accumulating adjacent to the blade is transported away from the blade area by a toner transport arrangement or by gravity. Blade cleaning is advantageous over other cleaning systems due to its low cost, small cleaner unit size, low power requirements, and simplicity. However, cleaning blades are primarily used in a static mode. The blade is either interference loaded or force loaded and remains in the operating position throughout the start-operate-stop cycle (“operating cycle”) of completing printing jobs. The static mode shortens the life of cleaning blades due to failures brought about from interaction with the photoreceptor chiefly at the beginning and ending of the operating cycle. Photoreceptor surface coatings while improving photoreceptor life typically results in far higher blade wear rates due to an increase in the coefficient of friction. A higher friction coefficient against the cleaning blades leads to increased torque and scratching problems. These problems can also contribute to future cleaning problems of toners from a photoreceptor surface.
Cleaning blades are typically designed to operate at either a fixed interference or fixed blade load as disclosed in U.S. Pat. No. 5,208,639 which is included herein by reference. Because of blade relaxation and blade edge wear over time, part and assembly tolerance, and cleaning stresses from environmental conditions and toner input, the cleaning blade is initially loaded to a blade load high enough to provide good cleaning at extreme stress conditions for all of the blade's life. However, a higher than required blade load causes the blade and charge retentive surface to wear more quickly. Overcoated charge retentive surfaces have been developed to reduce the wear rate. While an overcoat protects the charge retentive surface, the overcoats frequently increase the wear rate of the blades.
In interference loading, the blade is hard mounted to a frame to create the blade load against the photoreceptor. Over time the blade material relaxes and the blade load decreases somewhat from its initial value. Force loaded blades are mounted on a pivoted blade holder. The blade load is created by a weight or spring pressing against the blade holder that transmits a force to the blade tip. Over time the blade material creeps and the working angle is reduced somewhat from its initial value. Further, increases in friction due to blade age, lubrication depletion, and hardened toner lodged in the surface adds to blade stress further diminishing its effectiveness. Pivoted blade holders have traditionally been designed with their pivots located on the plane of blade tip contact. With this arrangement, the friction force, in the plane of tip contact acts through the pivot point and does not create a moment around the pivot and thus prevents any changes in blade normal load. As a consequence traditional blade holders do not take advantage of the variations in blade load caused by changes in the coefficient of friction.
Alternatives for operating a cleaning blade in high friction conditions have included methods to reduce the blade-photoreceptor friction, increasing the available torque to drive the photoreceptor, increasing the strength of the blade and optimizing cleaning blade parameters. Friction reduction concepts include additional developed toner (e.g., stripes developed in the inter-document zones), lubricating additives in the toner (e.g., zinc stearate), lubricating additives in the photoreceptor surface (e.g., PTFE), lubricating additives in the blade, and application of additives directly to the photoreceptor surface (e.g., zinc stearate). Historically friction reduction concepts have been marginally successful in very high friction conditions. Lubricating toner additives, PTFE photoreceptors and zinc stearate applicators have been the most successful alternatives. Increasing photoreceptor drive motor torque can avoid the photoreceptor stall problem with high friction, but unless blade life requirements are quite short, blade edge damage will still be an issue. Current blade materials have evolved to the point where little opportunity exists for significant increases in strength and blade life under high friction conditions. Harder blade materials may provide some life advantage and they typically have lower friction coefficients, but the improvement from blade material is unlikely to be sufficient by itself. Lower cleaning blade working angles, lower blade loads and optimized cut angles can provide some benefit in reducing blade edge stress, but again, probably not enough to solve a high friction problem alone. All of these alternatives involve some trade-off to obtain the improved blade life and lower photoreceptor drive torque, especially system interactions with the addition of lubricants. The pivoting blade concept provides a very significant reduction in photoreceptor drive torque and blade edge stress and can be combined with many of these alternatives for even greater improvements.
For the reasons stated above, and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification there is need in the art for a cleaning system that adapts to increases friction by decreasing blade load.